7 IS MEDUSAE OF THE WOULD. 



Star-like fossil, and sometimes two stars are joined by a single lobe. It appears to have been 

 gregarious, for Walcott records 42 specimens on a slab ot slate ij by 62 inches. There is of 

 course no proof that these fossils are those of medusae. 



Rbizostomites admirandus Haeckel. 



Rfiizosiomitrs admiranjus, Haeckel, 1866, Ncurs Jalirbuch fur .Min, Gcol. urni Palcuntol., p. 261, laf. 5; i869,Zeit.fiJr wissen. 

 Zool., Bd. 19, p. 557; 1S80, Syst. dcr .Medusen, p. 647. — Brandt, 1871, Mi'm. Acad. In-.p. Sci., .St. Pptersbourg, scr. 7, 

 tome 16, p. I, planchc I, figs. 1-4. — von .Ammon, 1886, Abhandl. Math.-phys. Classf, .Akad. Wissen Miinchen, Bd. 15, 

 p. 123, 158, i6^, taf. 2, fig. 2. — Walcott, 1898, Monographs U.S. Gcol. Surv., vol. 30, p. 76, plates 40, 42. — Maas, 1902, 

 Palaeontographica, Bd. 48, p. 306, taf. 23, fig. 2. — von Ammon, 1908, Gconostischt-n Jahresheftcn, Jahrg. 19, p. 174, fig. 1. 



von Ammon, who has made the most thorough stud)- of this fossil from the Jurassic 

 lithographic limestone of Solcnhofen and of Eichstadt, Bavaria, has decided that it is 

 identical with Haeckel's Rhizostoinites lithographicus, and that Leptobrac kites trigonohracliius 

 is probably the same medusa turned over on its side. He also concludes that Haeckel's Hexa- 

 rhizites itisignis is only a 6-rayed aberration of the same medusa. A thorough review of the 

 literature of this subject and e.\cellent figures are presented b)' Walcott, 1898, loc. cit. 



According to von Ammon and \\ alcott the disk in Rhizoslomitcs is round and as large 

 as 400 mm. in diameter, with 4 to 8 principal lobes and about 128 small marginal lappets of 

 various sizes, and indentations of the bell-rim marking the places of the 8 marginal sense- 

 organs. No marginal tentacles. A wide zone of circular muscles in the subumbrella, unbroken 

 in the rhopalar radii. 16 radial-canals, 8 rhopalar and 8 inter-rhopahu ; and a circular canal in 

 the external third of the umbrella. A strongly marked, circular depression between the muscle- 

 zone and the arm-disk may indicate an inner ring-canal. 4 not very wide subgenital ostia, 

 with 4 opercula forming lappets. Probably 8 long, thin mouth-arms with crinkled appen- 

 dages, and apparenth' with a tassel-shaped tuft at the lower end. 



This is undoubtedl\- a Rhizostomous medusa which appears to belong to an extinct genus 

 related to the modern Rhizostomata tnptera or lortfera. Maas, 1902, gives a remarkabh' clear 

 photograph of the margin showing one of the sense-organs, and he discusses the probable 

 form of the gonads. 



Brooksella alternata Walcott. 



Brookittla alurnaia, Walcott, 1986, Proc. V. S. Nat. Mus., vol. 18, p. 612, plate 31, figs. 1-5; 1898, Monographs U. S. Geol. 

 Surv., p. 23, plates 1-4. 



This fossil from the middle Cambrian shale from Coosa Valley, Alabama, is supposed to 

 be that of a medusa. They are 40 to 50 mm. in diameter. From 5 to 20, usually 5 to 8, more 

 or less distinct marginal lobes. No tentacles. A simple radial-canal in each lobe of the 

 umbrella. Oral plate quadripartite with 4 oral arms arising from it. Central stomach well 

 developed, hut apparenti)' there was no central niouth-opeiiing. 



This form was possibly allied to the Rhizostomae and ma\ ha\e had habits similar to those 



of Cassiopea. 



Brooksella confusa Walcott. 



BroohteUa confusa, Walcott, 1896, Proc. U. S. Nat. Mus., vol. 18, p. 612, plate 31, figs. 7a-b; 1898, Monographs U. S. Geol. 

 Surv., vol. 30, p. 30, plate 3. 



In Brooksella confusa the marginal lobes do not unite at the center ot the bell but join 

 irregularh', whereas in li. altcrtuiia the\' radiate from the center of the disk. I'his fossil is 

 found in the middle Cambrian shale of Coosa Valley, Alabama. 



Brooksella rhenana Kinkelin. 

 KiNKiLiN, 1903, Bericht .Senckcnberg Naturf. Grsell., Thcil 2, p. 89, taf. 1, fign. 1, 2. 



An 8-lobed medusa from the middle Devonian ot Ruplach. Onh' one specinun, showing 

 its exumbrella, was found, and this appears to me to be identical with, or at any rate very 

 closeK related to, Walcott's Brookstllti tilteniatti. 



